Human immunodeficiency virus (HIV) is a lentivirus that causes the acquired immunodeficiency syndrome (AIDS). This disease, first recognized in the early 1980s, is now a world-wide pandemic, with over 33 million people infected with HIV and the cause of over 1.8 million deaths per year. Untreated HIV infection results in progressive destruction of the immune system, resulting in opportunistic infections that contribute significantly to morbidity and mortality. Antiretroviral drugs must be taken for life because the virus establishes a latent state. Efficacious vaccines against HIV are not yet available. Several species of Asian macaques are susceptible to development of immunodeficiency following experimental infection with simian immunodeficiency virus (SIV), a virus genetically related to HIV. Accordingly, SIV infection of macaques serves as an important animal model for AIDS, including research on pathogenesis, host immunity, vaccinology, and anti-viral chemotherapy. Several groups in the CIID work with this model, including the Miller Laboratory, which focuses on mechanisms of entry in the female genital tract, approaches to prevention, mucosal immunity, and vaccine development. The Luciw Laboratory is involved in studying the molecular mechanisms of viral pathogenesis and development of novel anti-viral drug strategies to eliminate latent/persistent virus. The Barry Laboratory develops cytomegalovirus (CMV) vectors expressing SIV genes as potential attenuated viral vaccines in the macaque model.